1. Field of the Disclosure
Embodiments disclosed herein relate generally to drilling rigs. More particularly, embodiments disclosed herein relate to power limiting control systems on a drilling rig.
2. Background Art
A drilling rig is used to drill a wellbore in a formation. Drilling rigs may be large structures that house equipment used to drill water wells, oil wells, or natural gas extraction wells. Drilling rigs sample sub-surface mineral deposits, test rock, soil and groundwater physical properties, and may also be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs may be mobile equipment mounted on trucks, tracks, or trailers, or more permanent land or marine-based structures (such as oil platforms). The term “rig,” therefore, generally refers to a complex of equipment that is used to penetrate the surface of the earth's crust.
Referring to FIG. 1, a conventional drilling rig 30 is shown. Drilling rig 30 includes a derrick 14, which provides a support structure for a majority of the equipment used to raise and lower a drillstring 25 into and out of a wellbore. The drillstring 25 may be an assembled collection of drillpipe, drill collars, or any other assortment of tools, connected together and run into the wellbore to facilitate the drilling of a well (drillpipe 16 is shown in joints prior to being connected together).
The drillstring 25 may be raised and lowered into and out of the wellbore by the draw-works 7, which includes a spool powered by a motor or other power source 5. A drill line 12, which may be a thick, stranded metal cable, is run from the draw-works 7 over a crown block 13 and down through a travelling block 11. Typically, the crown block 13 remains stationary while the travelling block 11 moves vertically with the drillstring 25. The combination of the crown block 13 and the travelling block 11 provides a significant mechanical advantage for lifting the drillstring 25. Further, a swivel 18 may be attached to the travelling block 11 to allow rotation of the drillstring 25 without twisting the travelling block 11.
The drilling rig 30 further includes a rotary table 20 mounted in a rig floor 21, which is used to rotate the drillstring 25 along with a kelly drive 19. Kelly drive 19, attached at an upper end to the swivel 18 and at a lower end to the drillstring 25, is inserted through the rotary table 20 to rotate the drillstring 25 (drillstring rotation shown by arrow “R”). Kelly drive 19 may be square, hexagonal, or any other polygonal-shaped tubing and is able to move freely vertically while the rotary table 20 rotates it. Alternatively, drilling rig 30 may include a top drive (not shown) in place of kelly drive 19 and rotary table 20. Additionally, blowout preventers (“BOPs”) may be located below the rig floor 21 and installed atop a wellhead 27 to prevent fluids and gases from escaping from the wellbore. An annular BOP 23 and one or more ram BOPs 24 are shown and are commonly understood in the art.
During drilling operations, drilling fluid may be circulated through the system to carry cuttings away from the bottom of the wellbore as drilling progresses. Drilling fluid may be stored in mud tanks 1 before being drawn through suction line 3 by mud pumps 4. Drilling fluid (drilling fluid route is indicated by arrows “F”) is then pumped from mud pumps 4 through a hose 6, up a stand pipe 8, through a flexible hose 9, and down into the wellbore. Drilling fluid returning from the wellbore is routed through a flow line 28 to shakers 2, which are used to separate drill cuttings from the drilling fluid before it is pumped back down the wellbore.
A powering system, which in most modern rigs includes diesel generators (not shown), provides power for all of the machinery on the drilling rig. The powering system may typically include from one to six (or more) diesel generator units depending on the power requirements of the machinery on the drilling rig. The hoisting system (draw works 7), the circulating system (mud pumps 4), and the rotating system (top-drive or rotary table 20) are the major power consumers on the drilling rig, and these systems may subsequently be collectively referred to as the “tools.” Those skilled in the art will understand additional power consuming machinery may be on the drilling rig as well.
During operation of the drilling rig, there may be situations when the power requirement of the tools exceeds the power generation capacity of the generators (also referred to as an “overload condition”), which may lead to power shutdowns or blackouts on the drilling rig. Alternatively, power generation capacity of the generators may also suddenly decrease if a generator shuts down (or goes offline), which also may lead to an overload condition.